Abstract:As part of a wider study of floodplain vegetation along the River Murray, we carried out a field survey in 1987-1988 involving collection of floristic and vegetation condition data from 335 sample plots (each 400 m 2 in area), between Hume Dam and Lake Alexandrina (including the Edward-Wakool anabranch system). The floodplain vegetation is dominated by just two tree species, River Red Gum (Eucalyptus camaldulensis) and Black Box (Eucalyptus largiflorens), but the composition of the understorey shows much greater variation, both along the river and across the floodplain. A total of 499 plant species, subspecies and varieties were recorded from the survey plots, of which 316 (63%) were native and 183 (37%) were exotic. From analysis of the floristic data we identified 37 vegetation communities, not including the vegetation of permanent wetlands and cleared areas; 21 communities were distinguished in the River Red Gum zone, 12 communities in the Black Box zone, and 4 communities on rises within the floodplain. The main floristic division among the River Red Gum communities was between Riverine Plain/ Headwaters Zone communities of the upper Murray, and Mallee Zone communities of the lower Murray. Among the Black Box communities, the main floristic division was between inner floodplain communities and outer floodplain communities, with a further division between South Australian communities and New South Wales/Victorian communities. Major factors influencing the floristic patterns included flooding frequency/duration and soil salinity.Eucalypt health declined steadily downstream and was poorest in the lower reaches of the river below the Darling Junction, where 60% of the trees were healthy, 18% unhealthy (at least 40% of the canopy dead) and 22% dead. By comparison, at the upper end of the river, above Tocumwal, 84% of the trees were healthy, 14% unhealthy and only 2% dead. Overall, the condition of Black Box trees (44% unhealthy or dead) was worse than the condition of River Red Gum trees (29% unhealthy or dead). Eucaypt regeneration was also poorest below the Darling Junction, with regenerants present in 77% of plots upstream of the Darling but only 35% of plots downstream. The findings of poor tree health and sparse regeneration below the Darling coincide with the most heavily regulated part of the Murray, where the reduction in flooding due to upstream storages and water extraction, mainly for irrigation, has been greatest. Black Box regeneration was much sparser overall than River Red Gum regeneration (regenerants present in 69% of River Red Gum plots but only 29% of Black Box plots). The poor condition of the Black Box trees, coupled with their poor regeneration, suggests that the long-term future of this species along the Murray, particularly below the Darling Junction, is tenuous, even though it is a dominant component of the vegetation.The integrity of floodplain vegetation along the Murray has been severely compromised by weed invasion. Weeds were common throughout the survey area, but were most ...
Plant community and soil development were investigakl on oil/gas drilth~g sites occupying hotb sagebrush and coniferous forest vegetation types in northw&em Wyoming. sites ranged from 3 to 33 years in age since abandonment. Some sites were seeded at abandonment, wbile others revegetakd naturally. Vegetation and soils were sampled and compared on distorhed and ad]acent undisturbed sitea. Both soils and vegetation were lltaed by drilling activities. Disturbed soils generally had higher bulk density and pH and lower organic matter content than ulistorbed soils. AU disturbed sites were vegetationally dissboilar to adjacent native sites. However, sagebrush disturbances were progressing toward undisturbed conditions more rapidly than coniferous forest disturbancea. seeding accelerated vegetation development, although at different rates between sagebrush and coniferous forest d&turbanceu. Seeding and establishment of introduced grass species on dkturbed sites did not prevent natural recolonization of native speck Key Words: oil/gas drilling, reclamation, succession, soil development Oil and gas exploration and production can have major impacts on rangelands and forest lands in the western United States. Reclamation of drill sites and ancillary disturbances is not only essential for alleviating such impacts, but is required by law. Studies have been conducted within various ecosystems to determine the time required for natural revegetation after disturbance. Estimates of recovery have ranged from as little as 40 years for sagebrush communities (Tisdale and Hironalca 1981) up to 200 to 300 years for climax spruce-fir forests (Ronco 1976). This and other research (Judd 1940, Antos and Shearer 1981, Brown et al. 1976) suggest that reclamation techniques are necessary to accelerate plant community succession on disturbed lands, if recovery within a reasonable time frame is desired. Much research has been conducted to characterize plant succession on disturbed lands and to identify factors controlling this process (e.g., Skilbred 1979, Doerr et al. 1984, Sindelar 1978, Jaynes and Harper 1978). Unfortunately, lands impacted by oil and gas exploration have received little emphasis in such research. These lands differ from many other disturbances because of the small-sized, often scattered and environmentally disparate nature of individual drill sites, and the necessity of extensive access road SystemS. This project was conducted to evaluate succession on abandoned petroleum drill sites as influenced by time and a range of physical and biological factors. Specific objectives were to: (1) Evaluate the influence of surrounding vegetation, (2) Determine the effects of seeding vs. natural revegetation, and (3) Evaluate the influence of disturbance-induced edaphic changes, on plant community development.
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